In a medium-sized pot, melt the oil and butter over low-medium heat
Turn the heat down to low, add the marshmallows, vanilla, and sea salt, and stir until the marshmallows are melted and the mixture is smooth
Once thoroughly combined, turn the heat off and gradually fold in the cereal until it’s all coated*
Let the cereal and marshmallow mix cool for a few minutes before adding the rocky road mix-ins, then gently incorporate the marshmallows, chocolate chunks, and walnut pieces – be careful not to overmix as you don’t want the chocolate or marshmallows to completely melt, you want nice, gooey pockets!
Transfer to a dish – an 8x8 or 9x9 pan works well – lined with wax paper, then using the butter wrapper, wet fingers, or an oiled rubber spatula to prevent sticking, lightly press and spread the mixture into the dish (the harder you press, the denser the treats will be)
Allow the treats to cool for about an hour, then cut into squares, and store in an airtight container*